Vertebral compression fractures (“VCF”) represent a common spinal injury and may result in prolonged disability. Generally speaking, VCF involves collapsing of one or more vertebral bodies in the spine. VCF usually occurs in the lower vertebrae of the thoracic spine or the upper vertebrae of the lumbar spine. VCF generally involves fracture of the anterior portion of the affected vertebral body. VCF may result in deformation of the normal alignment or curvature, e.g., lordosis, of the vertebral bodies in the affected area of the spine. VCF and/or related spinal deformities may result, for example, from metastatic diseases of the spine, from trauma or may be associated with osteoporosis. Until recently, doctors were limited in how they could treat VCF and related deformities.
Recently, minimally invasive surgical procedures for treating VCF have been developed. These procedures generally involve the use of a cannula or other access tool inserted into the posterior of the targeted vertebral body, usually through the pedicles.
In one such procedure, a cannula or bone needle is passed through the soft tissue of the patient's back. Once properly positioned, a small amount of polymethylmethacrylate (PMMA) or other orthopedic cement is pushed through the needle into the targeted vertebral body. This technique may be effective in the reduction or elimination of fracture pain, prevention of further collapse, and a return to mobility in patients. However, this technique typically does not reposition the fractured bone into its original size and/or shape and, therefore, may not address the problem of spinal deformity due to the fracture.
Other treatments for VCF generally involve two phases: (1) reposition, or restoration of the original height of the vertebral body and consequent lordotic correction of the spinal curvature; and (2) augmentation, or addition of material to support or strengthen the fractured or collapsed vertebral body.
One such treatment involves inserting, through a cannula, a catheter having an expandable member into an interior volume of a fractured vertebral body, wherein the interior volume has a relatively soft cancellous bone surrounded by fractured cortical bone therein. The expandable member is expanded within the interior volume in an attempt to restore the vertebral body towards its original height. The expandable member is removed from the interior volume, leaving a void within the vertebral body. PMMA or other filler material is injected through the cannula into the void to stabilize the vertebral body. The cannula is then removed and the cement cures to augment, fill or fix the vertebral body.
Another approach for treating VCF involves inserting an expandable mesh graft balloon, or containment device, into the targeted vertebral body. The graft balloon remains inside the vertebral body after it is inflated with PMMA or an allograft product, which limits intraoperative loss of height of the repositioned endplates.
In some cases of fractured or otherwise damaged bones, bone grafts may be used to repair or otherwise treat the damaged area. In the United States alone, approximately half a million bone grafting procedures are performed annually, directed to a diverse array of medical interventions for complications such as fractures involving bone loss, injuries or other conditions necessitating immobilization by fusion (such as for the spine or joints), and other bone defects that may be present due to trauma, infection, or disease. Bone grafting involves the surgical transplantation of pieces of bone within the body, and generally is effectuated through the use of graft material acquired from a human source. Human graft material is primarily utilized due to the limited applicability of xenografts, e.g., transplants from another species.
Many orthopedic procedures involve the use of allografts, which are bone grafts from other human sources (normally cadavers). Allografts, for example, are placed in a host bone and serve as the substructure for supporting new bone tissue growth from the host bone.
The various bones of the human body such as the femur (thigh), tibia and fibula (leg), humerus (upper arm), radius and ulna (lower arm) have geometries that vary considerably. The lengths of these bones are varied, as well as the shape of the cross section of each type of bone and the shape of any given bone over its length. In addition, the wall thickness may vary in different areas of the cross-section of each bone. Thus, the use of any given bone to produce an implant or a component of an implant may be a function of the donor bone's dimensions and geometry. Machining of bones, however, may permit the production of an implant or a component of an implant with standardized or custom dimensions. Further, the availability of allograft bone source material is limited and the ability to enhance the bone yield from the available supply of allograft bone material is desirable.
As shown in FIG. 9 and as generally described in U.S. patent application Ser. No. 11/633,131, entitled “Flexible Elongated Chain Implant and Method of Supporting Body and Tissue With Same”, the entire contents of which are hereby incorporated by reference, a prior art flexible chain implant 1000 may include a plurality of bodies 1010 and a plurality of linking portions 1020 (sometimes referred to as struts, bridges or links). The implant 1000 comprises a single flexible monolithic chain having a first end 1002 and a second end 1004 formed of allograft cortical bone having a plurality of substantially non-flexible bodies connected by substantially flexible links. Such an implant 1000 may be utilized to treat VCF.
Thus, it is desirable in the art to provide safe and effective implants and methods for aiding and/or augmenting fractured or otherwise damaged vertebral bodies and other bones, preferably implants that may be inserted via a minimally invasive surgical technique. Moreover, where the implant is formed from bone, it is desirable to provide implants that are designed to enhance existing bone yield while minimizing discarded excess material.